Autoimmune and chronic inflammatory conditions together affect an estimated 5-10% of the population in Western countries and thus represent an enormous public health challenge. Our laboratory has focused on the role of the hyaluronan binding form of CD44 (CD44act) in an adhesion pathway leading to extravasation of activated T cells at target sites of autoimmunity. We have established that antigen driven induction of CD44act in lymphoid tissues arms T cells with a primary adhesion mechanism for capture at peripheral sites of inflammation, where hyaluronan is upregulated on endothelium in vascular beds exposed to proinflammatory stimuli. We have demonstrated a striking concordance of CD44act bearing T cells directly with inflammatory episodes in human autoimmune conditions and more recently have shown that CD44act expression is strikingly correlated with superior suppressor activity in CD4CD25+ regulatory T cells, in contrast to other known Treg markers. CD44act expression readily discriminates Treg with enhanced suppressive function in vitro and in several in vivo mouse models. Moreover, our recent data demonstrating isolation of the rare endogenously expressing CD44act population in human autoimmune conditions (Rheumatoid Arthritis and Inflammatory Bowel Disease) closely recapitulates the findings in the mouse, marking an expandable subset with potent regulatory activity. We hypothesize that this form of CD44 has great potential as a marker of functionally superior Treg, and for identifying those Treg endogenously generated via stimulation by (auto)antigen. They may therefore represent the most relevant Treg for disease control and for individualized patient specific cellular therapy in a spectrum of autoimmune and chronic inflammatory conditions. Moreover, since CD44act in principle would mark that segment of the Treg repertoire relevant to disease, broad immunosuppression and its attendant toxicities could be reduced or avoided. Finally, the propensity of this Treg population to activate CD44 suggests that this adhesion pathway is utilized for trafficking to target sites, and therefore has implications for efficient targeted delivery of Treg as well. We propose to 1) Perform in depth functional and phenotypic characterization of in vitro expanded CD44act-positive Treg derived from patients with autoimmune disease;2) Characterize and expand Treg isolated directly ex vivo from surgical tissue of IBD patients and compare to those found in peripheral blood;3) Determine the role of the active, ligand-binding form of CD44 on CD4CD25+ Treg in trafficking to sites of inflammation in a mouse model of human disease and define adhesion mechanisms of traffic;4) Examine the utility of in vitro expanded CD44act-positive Treg isolated from affected animals in murine colitis. These studies should allow a determination of whether this marker provides a novel tool for identifying desired specific regulatory activity, enriching for maximal suppressor potency in a vastly heterogeneous T cell population in clinical settings, and whether CD44act contributes to arming these relevant Treg with appropriate molecules for trafficking to target sites. PUBLIC HEALTH RELEVANCE: Autoimmune diseases (for example, rheumatoid arthritis) affect millions of individuals worldwide and thus represent a significant health challenge. Both the damage and control processes in autoimmune disease involve special white blood cells (T cells) able to enter surrounding tissue from the bloodstream. The purpose of this study is to investigate a specialized molecule (CD44) that better directs those T cells that protect against autoimmunity into the target tissues, thereby preventing and lessening disease. Understanding the role of this receptor will permit the design of interventions and therapies in a variety of autoimmune diseases.